TF-3674 Add ADR for logic reply email

Signed-off-by: dab246 <tdvu@linagora.com>

docs/adr/0065-logic-for-reply-email.md

@@ -0,0 +1,98 @@
+# 65. Logic for reply email
+
+Date: 2025-04-21
+
+## Status
+
+Accepted
+
+## Context
+
+- The email reply logic is quite complex so to avoid mistakes and regression of errors later.
+
+## Decision
+
+Brief the logic flow to easily follow changes during email reply process:
+
+**1. Reply:**
+
+- If the user is the `sender`
+
+```console
+To = email.to
+Cc, Bcc, ReplyTo = Empty
+```
+
+- Otherwise, If the email has a `List-Post` header then:
+
+```console
+To = email.from.withoutUser
+Cc, Bcc, ReplyTo = Empty
+```
+
+- Otherwise, If the email without a `List-Post` header, `email.replyTo` is not empty then:
+
+ ```console
+To = email.replyTo.withoutUser
+Cc, Bcc, ReplyTo = Empty
+```
+
+- Otherwise:
+
+```console
+To = email.from.withoutUser
+Cc, Bcc, ReplyTo = Empty
+```
+
+**2. Reply To List:**
+
+- If the email has a `List-Post` header then:
+
+```console
+To = email.List-Post.withoutUser
+Cc, Bcc, ReplyTo = Empty
+```
+
+- Otherwise: There is no `Reply To List` feature
+
+3. Reply all
+
+- If the user is the sender
+
+```console
+To = email.to.withoutUser
+Cc = email.cc.withoutUser
+Bcc = email.bcc.withoutUser
+ReplyTo = email.replyTo.withoutUser
+```
+
+- Otherwise, If the email has a `List-Post` header then:
+
+```console
+To = (email.replyTo + email.from + email.to).withoutUser
+Cc = email.cc.withoutUser
+Bcc = email.bcc.withoutUser
+ReplyTo = Empty
+```
+
+- Otherwise, If the email without a `List-Post` header, `email.replyTo` is not empty then:
+
+```console
+To = (email.replyTo + email.to).withoutUser
+Cc = email.cc.withoutUser
+Bcc = email.bcc.withoutUser
+ReplyTo = Empty
+```
+
+- Otherwise
+
+```console
+To = (email.from + email.to).withoutUser
+Cc = email.cc.withoutUser
+Bcc = email.bcc.withoutUser
+ReplyTo = Empty
+```
+
+## Consequences
+
+- Any changes to reply email should be updated in this ADR.